1. Field of the Invention
The present invention relates to a device for the coupling of two cylindrical parts, especially to form compound tools.
2. Description of the Related Art
The term "compound tools" should be understood to refer to conventional chip-removing tools such as drill bits, cylindrical cutters or taps, which in order to be used in a machine tool must be assembled with a cone element that is inserted into the chuck of the machine.
To enable the same tool to be used for different chip-removing operations, it is often necessary to provide the cone element and the chip-removing tool with one or more extensions: these consist of cylindrical constructional elements which must be coupled together rigidly and with the greatest precision.
It is known in the state of the art to join one end of one cylindrical body having a seat to a projection provided on the other cylindrical body, thus enabling the two extensions to be joined by means of a male-female coupling.
To achieve a firm connection, in the known device the projecting part is first inserted into the cavity of the adjacent cylindrical part and then locked in position with the aid of screws or grub screws inserted transversely into the two cylindrical bodies to be assembled.
In one known embodiment, inside the coupling pin is a small cylinder with conical ends. These ends engage with the abovementioned transverse grub screws, which likewise have conical ends and therefore, when the two traverse locking grub screws are screwed home, the projecting pin is locked inside the cavity receiving it. During the tightening, the two parallel end surfaces of the cylindrical bodies are tightened together, creating the extension for the tool.
In the known embodiment, a problem has been encountered in that the area of contact between the two cylindrical bodies is formed by two surfaces parallel with each other and perpendicular to the longitudinal axis of the cylindrical bodies being assembled; a fact which does not eliminate the danger of transverse movements and hence of the axes of the cylindrical bodies coming apart.
Furthermore in the known embodiment it has been found that because the angle of the cone of the locking grub screws assumes an angle of 45.degree. to the longitudinal axis of the coupled cylindrical bodies, and therefore the force with which the locking grub screws are tightened is translated into an equal locking force. Since the force with which the locking grub screw is screwed in cannot be increased at will lest the thread be damaged, the locking force applicable between the two cylindrical bodies is accordingly limited, even though a greater locking force would increase the rigidity of the coupling of the two cylindrical bodies.
A further problem with the known embodiment is observable in the fact that, if wear develops in either the pin or the cavity forming the male-female coupling, the cylindrical bodies may move reciprocally along the parallel coupling surfaces, which is a cause of imprecise machining.
Finally, the known device requires the use of two locking screws or grub screws for the assembly stage. This not only increases the number of constructional elements needed, but also requires careful and balanced tightening of the two locking grub screws. In addition, these locking elements must be removed while the pin and cavity are being joined together, and then reinserted afterwards.